1. Field of the Invention
This invention relates to the disinfection of medical apparatus; more particularly to the disinfection of heat- and liquid-sensitive medical apparatus by the use of isopropanol in the vapor phase.
2. Description of the Prior Art
Conventional hospital sterilization practices call for the use of steam or ethylene oxide gas. There are limitations, however, on the types of equipment that may be subjected to these sterilants. Steam may cause damage to heat-sensitive materials such as plastics, rubber and the like. Ethylene oxide gas sterilization, while carried out at lower temperatures than steam sterilization, generally requires a relatively long aeration period or "turn-around time". Certain types of medical apparatus, especially expensive items, cannot be out of service for that period of time. As to this latter apparatus, when steam sterilization is also prohibited because of material limitations, the hospital generally resorts to the manual application of liquid disinfectants. Even this procedure has serious drawbacks, however, because parts of an instrument being disinfected in such manner may be subject to chemical attack and/or other degradation by the liquid disinfectant, especially when immersion is used as the application technique.
Specific types of medical apparatus that are not subject to steam and/or ethylene oxide gas sterilization for the reasons mentioned above include endoscopes, respiratory therapy equipment and anesthesia equipment, wrapped or unwrapped.
Endoscopes are instruments for the visual examination of body cavities, such as bronchoscopes, laparoscopes, arthoscopes, and upper and lower GI endoscopes. Fiberscopes or flexible fiberoptic endoscopes are those endoscopes having fiberoptic lighting; these are particularly adapted to bending and generally provide a brighter light than standard endoscopes. Endoscopic accessory or related equipment includes cytology brushes and biopsy forceps used in gastrointestinal endoscopy. The need for efficient and effective disinfection and cleaning of endoscopic equipment has been highlighted due to infections related to use of this kind of equipment in hospitals. Nosocomial (hospital-acquired) infections have been specifically associated with inadequately cleaned respiratory equipment.
The Ad Hoc Committee of Infection Control in the Handling of Endoscopic Equipment, coordinated by the Association of Practitioners in Infection Control (APIC), in January 1978 established the following guidelines for the cleaning and disinfection of flexible fiberoptic endoscopes used in gastrointestinal endoscopy:
"1. Scrupulous mechanical cleaning of insertion tube and channels, using a detergent, is imperative. This must be done immediately after use to prevent the drying of secretions.
2. Inspection of equipment for damage.
3. Disinfection of endoscopic insertion tube and all channels, performed with a chemical substance having disinfecting action sufficient to kill all microorganisms (gram-positive and gram negative bacteria, fungi mycobacteria, and lipophilic and hydrophilic viruses) except bacterial spores when used according to manufacturer's instructions.
4. Adequate rinsing must follow such disinfection.
It should be emphasized that adequate rinsing is necessary to prevent possible residual toxic effects of the disinfectant chemical and/or detergent. The risks of toxicity with regard to particular disinfectants and/or detergents need further exploration.
5. The insertion tube and inner channels should be thoroughly and immediately air dried after cleaning and prior to storage. (Bacteria will multiply in a moist environment).
6. Instruments to be stored.
7. Ethylene oxide sterilization is not generally practical. If used, it is imperative that meticulous cleaning be accomplished as described in Guideline 1, and that it be followed by adequate aeration.
8. Because of the spring-like structural configuration, accessories such as biopsy forceps and cytology brushes have been shown to be extremely difficult to clean and disinfect. After immediate surface cleaning with a detergent/disinfectant, and rinsing, it is advisable to use either steam under pressure or gas (ethylene oxide sterilization) or any other treatment which has the capability of penetrating the spring-like structures.
It is emphasized that the heat treatments described be applied only to accessories such as biopsy forceps, not to fiberoptic devices. Improved structural configurations of the accessories and/or more efficient cleaning methods need further exploration."
These guidelines illustrate some of the special considerations and problems in disinfecting flexible fiberoptic endoscopes (fiberscopes). Liquid disinfectants, detergents, distilled water, steam and ethylene oxide gas (when possible), have thus been used in varying combinations to accomplish disinfection of this type of equipment. Even when disinfection has been adequate, time-consuming air drying is required and instruments are not immediately available for re-use. Presently, endoscopic equipment is either simply cleaned before re-use or is disinfected by immersion in some liquid biocidal agent. Simple cleaning is not an adequate process to protect against cross infection. While disinfecting by immersion in a liquid agent can be effective, it does not permit packaging of the item to protect it from recontamination, in handling, transit or storage. Furthermore, it often damages the device, and generally requires copious rinsing with sterile distilled water to remove the residual agent before use. Additionally, immersion and rinsing are at the discretion of the worker and are frequently inadequate. Liquids also exert a dissolving action on certain polyvinyl chlorides, silicones, acrylics, resins, lens cements and other materials of the endoscopes. Detergents can be abrasive and corrosive. The cumulative effects diminish the use-life of the equipment.
An optimum cleaning and disinfection process for endoscopes, including fiberoptic endoscopes and related equipment, would therefore incorporate the following features:
1. Operate at low temperatures
2. Operate at atmospheric pressure or below (vacuum)
3. Leave no residual chemical
4. Provide moisture-free articles following disinfection
5. Require no aeration time
6. Provide adequate penetration of springs and interstices by disinfectant
7. Provide adequate bactericidal action.
One object of this invention, therefore, is to provide a quick, penetrating, low-temperature treatment of articles at atmospheric pressure or below (vacuum) which destroys infectious organisms, yields essentially moisture-free articles without aeration time, and leaves no residual agent.
Another objective is to provide an efficient and uniform treatment for all endoscopic (including fiberoptic) and accessory equipment, as well as for other articles which cannot because of their structure or the materials of which they consist be sterilized by conventional methods, or cannot be disinfected by immersion.
Nathan U.S. Pat. No. 867,831 discloses the use of alcohol fumes to sterilize beer vessels. The vapors condense within a pressurized chamber during sterilization. The condensate will also dissolve resins formed in the beer-manufacturing process. These high pressure, moisture and resin-dissolving features, which are favorable to beer vessels, would damage endoscopic equipment.
Gibson U.S. Pat. No. 246,494 uses alcohol vapors and steam to restore feathers. This is also a high temperature, pressure process contraindicated for endoscopes.
Gartner U.S. Pat. No. 903,853 teaches the use of a methyl alcohol in approximately 55% concentration or ethyl alcohol and water vapor in large quantities. The sterilization cycle comprises essentially the following steps: (1) exhaustion of a sterilization chamber to a pressure-gauge vacuum of 700 mm; (2) introducing a mixture of water and methyl alcohol into the chamber and vaporizing the same; (3) a timed exposure (e.g., about 20 minutes) after vaporization is completed; (4) admission of air to atmospheric pressure; (5) all valved access to the chamber is closed and temperature is maintained constant for 11/2 hours from initiation of treatment; and, finally (6) a half-hour sweep of a strong current of air through the chamber. The articles are preferably subjected to pressure after completion of this complicated cycle. The teaching emphasizes the importance of large vapor quantity and exhausting the chamber of air to a high degree before introducing the disinfectant in order to accomplish disinfection. Thus biocidal activity is dependent on large quantities of alcohol and water vapors operating under a high vacuum. At 55% concentration, vapor biocidal activity without this extremely high exhaustion would be inadequate for disinfection. The large vapor quantities required would also penetrate and exert harmful dissolving action on synthetic endoscopic materials.
Thus the alcohols and methods of these patents are unsuitable for disinfection of endoscopic equipment in modern hospital practice.